The present invention relates to a nuclear magnetic resonance diagnosis apparatus; and, more particularly, the invention relates to a nuclear magnetic resonance diagnosis apparatus which is suitable for diagnosing a condition of an object to be inspected by obtaining an image and/or a nuclear magnetic spectrum of the object to be inspected using a nuclear magnetic resonance phenomenon.
In a conventional nuclear magnetic resonance diagnosis apparatus, a measurement system, including a magnet generating a static magnetic field, a gradient magnetic field coil, an irradiation coil generating a radio frequency magnetic field and a receiving coil for receiving a nuclear magnetic resonant signal from an object to be inspected, is installed in an electromagnetic shield room in order to shield radio frequency noises generated inside and outside the nuclear magnetic resonance diagnosis apparatus. A gradient magnetic field power supply for driving the gradient magnetic coil, a power amplifier for the irradiation coil and a signal amplifier for amplifying the nuclear magnetic resonance signal detected by the receiving coil are contained in individual cabinets, or in an integrated cabinet, and are connected to the gradient magnetic field coil, the irradiation coil and the receiving coil in the shield room through line filter units (line noise removing means) provided on the wall surface of the shield room, respectively.
The gradient magnetic field power supply, the power amplifier and the signal amplifier are connected to line filter units through respective cables, and the ground points of the cabinets or the constituent circuits are connected to a system ground common to the shield room. A nuclear magnetic resonance diagnosis apparatus of this type is described, for example, in Catalogue No. CP-E094 xe2x80x9cAIRISxe2x80x9d of Hitachi Medical Corporation and Catalogue No. CP-E090 xe2x80x9cSTRATISxe2x80x9d of Hitachi Medical Corporation.
The shield room and the line filter unit block remove radio frequency noises existing in the surrounding area and radio frequency noises generated by the nuclear magnetic resonance diagnosis apparatus itself outside the shield room so that the noises are not received by the measurement system in the shield room.
On the other hand, in recent years, the imaging technology in the field of nuclear magnetic resonance diagnosis has become increasingly faster in measuring speed and has been enhanced in function; and, accordingly, a power supply of a switching type capable of coping with a high gradient magnetic field and a high slew rate (for instance, above 100 T/m/s) has been used as the gradient magnetic field power supply. One disadvantage of a power supply of the switching type is that it generates wide band radio frequency noises, and there are some cases in which the radio frequency noises can not be sufficiently removed only by provision of the shield room and the line filter unit described above.
Since the shielding ratio of the shield room and the line filter unit is 60 dB to 80 dB (1/1000 to 1/10000), the noise becomes A/1000 to A/10000, where A is the intensity of the generated noise of the gradient magnetic field power supply. Therefore, the effect on the NMR signal can be neglected. However, since the shielding performance of the shield room and the line filter unit is the same even if the generated noise of the gradient magnetic field power supply is increased (for example, by as much as 10 times) due to high speed measurement, the noise becomes 10A/1000 to 10A/10000. Therefore, the effect of this noise on the NMR signal can not be neglected. Further, when the attenuation ratio of the line filter is increased in a case of using EPI (echo planer imaging) or the like, which can switch the operation of the gradient magnetic field power supply at a high speed, the switching waveform tends to lose its shape, changing from a pulse shape to a wave shape, so that the required imaging function can not be attained. This is also one of the reasons why the noise can not be removed.
Particularly, since the condition for arranging the units, such as the gradient magnetic field power supply, the radio frequency power amplifier, the radio frequency signal amplifier, and so on, varies depending on the place where the nuclear magnetic resonance diagnosis apparatus is installed, there are some cases in which the noises, particularly the noise of the gradient magnetic field power supply, can not be removed depending on the installation environment.
As another method of removing the radio frequency noise from the gradient magnetic field power supply, there is a method in which a filter of a low pass type having a high attenuation ratio for the measurement band of the nuclear magnetic resonance signal is added just near the output position, in addition to the line filter unit in the shield room. However, in this case, a higher peak electric power is necessary when an inductive type of filter is employed. When a capacitance type of filter is employed, there is a problem in that a high response characteristic having a rapid rise to a pulse output current is degraded; and, accordingly, it becomes difficult to obtain a flat top waveform having a good flatness for suppressing ringing at the rising portion.
An object of the present invention is to provide a nuclear magnetic resonance diagnosis apparatus which is suitable for reducing the effect of radio frequency noises on the nuclear magnetic resonance signal.
Another object of the present invention is to provide a nuclear magnetic resonance diagnosis apparatus which is suitable for removing the effect of radio frequency noises on the nuclear magnetic resonance signal without affecting the output response characteristic and the required electric power of the gradient magnetic field power supply.
According to the present invention, a nuclear magnetic resonance diagnosis apparatus is provided which comprises: a measurement system, including a magnet for generating a static magnetic field in a space in which an object to be inspected is placed, a gradient magnetic field coil for generating a gradient magnetic field in the space, an irradiation coil for applying a radio frequency magnetic field to the object to be inspected and a receiving coil for detecting a nuclear magnetic resonance signal generated from the object to be inspected; a gradient magnetic field power supply for driving the gradient magnetic field coil; a signal processing system for reconstructing a sectional image of the object to be inspected based on the nuclear magnetic resonance signal; an electromagnetic shield room in which the measurement system is arranged; a line noise filter connected between the gradient magnetic field coil and the gradient magnetic power supply; and a first cabinet in which the gradient magnetic field power supply and the line noise filter are contained, the first cabinet being mechanically and electrically connected to the shield room.
According to another aspect of the present invention, the nuclear magnetic resonance diagnosis apparatus further comprises a radio frequency amplifier for supplying a current to the irradiation coil; a signal amplifier for amplifying the nuclear magnetic resonance signal; and a second cabinet in which the radio frequency amplifier and said signal amplifier are contained, the second cabinet being mechanically and electrically connected to the shield room.
According to an additional aspect of the present invention, a nuclear magnetic resonance diagnosis apparatus is provided which comprises: a measurement system, including a magnet for generating a static magnetic field in a space in which an object to be inspected is placed, a gradient magnetic field coil for generating a gradient magnetic field in the space, an irradiation coil for applying a radio frequency magnetic field to the object to be inspected and a receiving coil for detecting a nuclear magnetic resonance signal generated from the object to be inspected; a gradient magnetic field power supply for driving the gradient magnetic field coil; a radio frequency amplifier for supplying a current to the irradiation coil; a signal amplifier for amplifying the nuclear magnetic resonance signal; a preamplifier connected between the receiving coil and the signal amplifier; an electric power supply for the preamplifier; a signal processing system for reconstructing a sectional image of the object to be inspected based on the nuclear magnetic resonance signal; an electromagnetic shield room in which the measurement system is arranged; a line noise filter connected between the gradient magnetic field coil and the gradient magnetic field power supply; and a line noise filter connected between the preamplifier and its electric power supply; a first cabinet in which the gradient magnetic field power supply and the line noise filter for the gradient magnetic field are contained, the first cabinet being mechanically and electrically connected to the shield room; and a second cabinet in which the radio frequency amplifier, the signal amplifier, the preamplifier and the line noise filter therefor are contained, the second cabinet being mechanically and electrically connected to the shield room; the gradient magnetic field power supply and the line noise filter for the gradient magnetic field being connected to each other so as to reduce the distance therebetween, and/or the preamplifier and the electric power supply for the preamplifier being connected to each other so as to reduce the distance therebetween.
According to yet another aspect of the present invention, a nuclear magnetic resonance diagnosis apparatus is provided which comprises: a measurement system, including a magnet for generating a static magnetic field in a space in which an object to be inspected is placed, a gradient magnetic field coil for generating a gradient magnetic field in the space, an irradiation coil for applying a radio frequency magnetic field to the object to be inspected and a receiving coil for detecting a nuclear magnetic resonance signal generated from the object to be inspected; a gradient magnetic field power supply for driving the gradient magnetic field coil; a radio frequency amplifier for supplying a current to the irradiation coil; a signal amplifier for amplifying the nuclear magnetic resonance signal; a preamplifier connected between the receiving coil and the signal amplifier; an electric power supply for the preamplifier; a signal processing system for reconstructing a sectional image of the object to be inspected based on the nuclear magnetic resonance signal; an electromagnetic shield room in which the measurement system is arranged; a line noise filter for the gradient magnetic field connected between the gradient magnetic field coil and the gradient magnetic field power supply; and a line noise filter for the preamplifier connected between the preamplifier and its electric power supply; the gradient magnetic field power supply and the line noise filter for the gradient magnetic field being connected to each other so as to be prevented from being spaced apart from each other, and/or the preamplifier and the electric power supply therefor being connected to each other so as to be prevented from being spaced apart from each other.
According to a further aspect of the present invention, a nuclear magnetic resonance diagnosis apparatus comprises: a measurement system, including a magnet for generating a static magnetic field in a space in which an object to be inspected is placed, a gradient magnetic field coil for generating a gradient magnetic field in the space, an irradiation coil for applying a radio frequency magnetic field to the object to be inspected and a receiving coil for detecting a nuclear magnetic resonance signal generated from the object to be inspected; a gradient magnetic field power supply for driving the gradient magnetic field coil; a radio frequency amplifier for supplying a current to the irradiation coil; a signal amplifier for the nuclear magnetic resonance signal; a preamplifier connected between the receiving coil and the signal amplifier; an electric power supply for the preamplifier; a signal processing system for reconstructing a sectional image of the object to be inspected based on the nuclear magnetic resonance signal; an electromagnetic shield room in which the measurement system is arranged; a line noise filter connected between the gradient magnetic.field coil and the gradient magnetic field power supply; and a line noise filter connected between the preamplifier and its electric power supply; the gradient magnetic field power supply and the line noise filter for the gradient magnetic field being connected to each other so that a connection line therebetween becomes substantially zero in impedance, and/or the preamplifier and the electric power supply therefor being connected to each other so that a connection line therebetween becomes substantially zero in impedance.
According to a further additional aspect of the present invention, a nuclear magnetic resonance diagnosis apparatus is provided which comprises: a measurement system, including a magnet for generating a static magnetic field in a space in which an object to be inspected is placed, a gradient magnetic field coil for generating a gradient magnetic field in the space, an irradiation coil for applying a radio frequency magnetic field to the object to be inspected and a receiving coil for detecting a nuclear magnetic resonance signal generated from the object to be inspected; a gradient magnetic field power supply for driving the gradient magnetic field coil; a radio frequency amplifier for supplying a current to the irradiation coil; a signal processing system for reconstructing a sectional image of the object to be inspected based on the nuclear magnetic resonance signal; an electromagnetic shield room in which the measurement system is arranged; a line noise filter connected between the gradient magnetic field coil and the gradient magnetic power supply; and a system ground to which the gradient magnetic field power supply, the signal amplifier, the radio frequency amplifier and the line noise filter are connected.
According to still another aspect of the present invention, a nuclear magnetic resonance diagnosis apparatus is provided which comprises: a measurement system, including a magnet for generating a static magnetic field in a space in which an object to be inspected is placed, a gradient magnetic field coil for generating a gradient magnetic field in the space, an irradiation coil for applying a radio frequency magnetic field to the object to be inspected and a receiving coil for detecting a nuclear magnetic resonance signal generated from the object to be inspected; a gradient magnetic field power supply for driving the gradient magnetic field coil; a signal processing system for reconstructing a sectional image of the object to be inspected based on the nuclear magnetic resonance signal; an electromagnetic shield room in which the measurement system is arranged; and a line noise filter connected between the gradient magnetic field coil and the gradient magnetic power supply; the gradient magnetic field power supply and the line noise filter being connected to each other so that a noise voltage generated from the gradient magnetic field power supply and mixed in the nuclear magnetic resonance signal is substantially zero.
Other objects and features of the present invention will become more apparent from the description of the preferred embodiments of the present invention taken in connection with the accompanying drawings.